949423 Volvo.Penta Screw

Engine Speed Governing
The ECM maintains the desired engine speed by controlling the actuator for the throttle. The actuator is at the inlet to the aftercooler. The actuator is electrically controlled and electrically actuated.The ECM issues a throttle command that represents a percent of the level of electrical current. The output can be viewed on the Caterpillar Electronic Technician (ET).Desired engine speed is determined by the following:
Status of the idle/rated switch
Desired speed input
Programmable ParametersAir/Fuel Ratio Control
The ECM provides control of the air/fuel mixture for performance and for efficiency at low emission levels. The system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The control compensates for changes in the BTU of the fuel to maintain desired emission levels.The following steps describe the basic operation:
The ECM determines the desired flow rates for the air and for the fuel. The flow rates are determined by these factors:
Desired engine speed
Actual engine speed
Calculated engine load
The command for the flow of the fuel is sent to the electronic fuel metering valve via the CAN data link.This process is repeated continuously during engine operation.Start/Stop Sequencing
The ECM contains the logic and the outputs for control of starting and of shutdown. The customer programmable logic responds to signals from the following components: engine control, emergency stop switch, remote start switch, data link, and other inputs.When the programmable logic determines necessary to crank the engine, the ECM supplies +Battery voltage to the relay for the starting motor. The ECM removes the voltage when the programmable crank terminate speed is reached or when a programmable cycle crank time has expired.The engine must be equipped with an energize-to-run type of gas shutoff valve (GSOV). The source of the voltage to the GSOV depends on the engine configuration. The GSOV may be energized by customer equipment or by the engine control system.If the engine control system controls the GSOV, the ECM supplies +Battery voltage to the GSOV whenever the programmable logic determines that fuel is required to operate the engine.For more information on programmable parameters, refer to Troubleshooting, "Programming Parameters".Engine Monitoring and Protection
The ECM monitors both the engine operation and the electronic system.Problems with engine operation such as low oil pressure produce an event code. The ECM can issue a warning, a derating, or a shutdown. This depends on the severity of the condition. For more information, refer to Troubleshooting, "Troubleshooting With An Event Code".Problems with the electronic system such as an open circuit produce a diagnostic code. For more information, refer to Troubleshooting, "Troubleshooting With A Diagnostic Code".Ignition Control
The ECM provides variable ignition timing that is sensitive to detonation.Each cylinder has an ignition transformer that is located under the valve cover for the cylinder. To initiate combustion, the ECM sends a pulse of approximately 100 V to the primary coil of an ignition transformer at the appropriate time and for the appropriate duration. The transformer steps up the voltage to create a spark across the spark plug electrode.Detonation sensors monitor the engine for excessive detonation. The engine has one detonation sensor for each pair of adjacent cylinders. The sensors generate data on vibration that is processed by the ECM to determine detonation levels. If detonation reaches an unacceptable level, the ECM retards the ignition timing of the affected cylinder or cylinders. If retarding the timing does not limit detonation to an acceptable level, the ECM shuts down the engine.The ECM provides extensive diagnostics for the ignition system. The ECM also provides a switch input for ignition timing to allow operation with alternate fuels such as propane that requires a timing offset.one detonation sensor for each pair of adjacent cylinders.